Calcium Manganese Oxides as Oxygen Evolution Catalysts: O₂ Formation Pathways Indicated by ¹⁸O‐Labelling Studies

Abstract

Oxygen evolution catalysed by calcium manganese and manganese-only oxides was studied in (18)O-enriched water. Using membrane-inlet mass spectrometry, we monitored the formation of the different O(2) isotopologues (16)O(2), (16)O(18)O and (18)O(2) in such reactions simultaneously with good time resolution. From the analysis of the data, we conclude that entirely different pathways of dioxygen formation catalysis exist for reactions involving hydrogen peroxide (H(2)O(2)), hydrogen persulfate (HSO(5)(-)) or single-electron oxidants such as Ce(IV) and [Ru(III) (bipy)(3)](3+) . Like the studied oxide catalysts, the active sites of manganese catalase and the oxygen-evolving complex (OEC) of photosystem II (PSII) consist of μ-oxido manganese or μ-oxido calcium manganese sites. The studied processes show very similar (18)O-labelling behaviour to the natural enzymes and are therefore interesting model systems for in vivo oxygen formation by manganese metalloenzymes such as PSII.

Nitrogen-doped carbon nanomaterials as non-metal electrocatalysts for water oxidation

“…Consequently, researchers have attempted to biomimic natural compounds, such as hybrids of CaMn 2 O 4 and Mn 3 O 4 /CoSe 2 , to obtain efficient OER electrocatalysts [13][14][15] . However, a nanocomposite of Mn 3 O 4 /CoSe 2 required an overpotential of approximately 0.45 V in potassium hydroxide (KOH) solution (pH 13) to achieve a current density of 10 mA cm À 2 (current density based on geometric surface area (GSA)) 15 .…”

Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

“…Because the capability for efficient water oxidation is unique to photosystem II among all biological photosystems (6,7), these CaMnO materials that mimic the elemental composition, manganese oxidation state, and particle size of the photosynthetic water oxidation center are of special interest (8)(9)(10)(11)(12). Although a number of other metal compounds function as water-oxidizing catalysts (13), many contain rare and expensive metals like iridium and ruthenium; the advantage of manganese oxides (Mn-oxides) is that they are earth-abundant, inexpensive, and environmentally friendly (1)(2)(3)(4)(5)14).…”

An Institutional Approach to Solar Fuels Research

“…[11][12][13][14][15] Other aspects that can still be learned from the biological systems are, for example, the efficient coupling of electron and proton transfer and the optimal geometry and electronic structure for O-O bond formation. Therefore, a tight interplay between researchers working on the biological processes and those developing man-made devices will contribute significantly to a faster development and implementation of devices for artificial photosynthesis.…”

“…The approach is two-fold: (a) understanding and improving natural photosynthesis, [9,11,[25][26][27] and (b) applying this knowledge to the construction of low cost, printable artificial membranes for the direct (wireless) conversion of solar energy into fuels. [12,66] This environment is led by the author.…”